This calculator requires the use of Javascript enabled and capable browsers. Though it does intensive math calculations, it is a close estimator and enables the user to approximate the amount (area) of wallpaper, number of rolls, and optionally trim, required for a given room, based on parameters entered. It calculates the square footage of surfaces requiring wallpaper, less that area occupied by doors or windows. Please remember that the calculation is approximate. It assumes the average door is 21 square feet in surface and the average window is 16 square feet. If you wish to use decorative trim, check the box. It calculates 1 trim strip; if you wish to use 2 or 3, double or triple the quantity of calculated decorative trim rolls as a result. Decorative trim is assumed to be at the ceiling and therefore is not hampered by doors or windows. The requirement (and subsequent cost) in actual use will change if positioned in the center of the wall or close to the floor because of doors and windows. Trim rolls are about 15 linear feet long. Enter the cost of the wallpaper per roll, double roll (about 55 square feet) or single roll (about 27 square feet), and the total price and the area of the wallpaper required is calculated. To do another, click the Clear Values button and then enter a new set of values. You may also wish to just change certain fields and recalculate. Calculated accuracy of current Javascript enabled browsers is generally 16 places. Please remember that due to cuts, patterns that need to be matched at cuts, and non-usable ends, wallpaper rolls are generally considered to be between only 85 and 95 percent usable. The smaller the pattern, the less the waste. Trim border rolls follow the same guideline, but are generally considered to have more waste since most people want an entire border without a cut on a wall. Obviously, walls longer than 15 linear feet require a longer roll, if possible, or will require a splice. When you buy wallpaper or wallcoverings, look for run numbers, lot numbers or run codings on the label or roll. These numbers should be the same on each roll. Wallcoverings are printed in large batches, and the colors can vary perhaps slightly, but nonetheless noticeably, between the batches. To avoid the risk of running out, and to make sure you have extras in case you need to patch an area, you may wish to buy an extra roll. To be sure you have enough wallcovering to cover the room, our calculator rounds up and calculates on the average USABLE quantity on a roll.